The present invention relates to an optical data record/reproduction apparatus which records and reproduces data into and from an optical record medium, such as an optical disk or an opto-magnetic disk, or which records, reproduces, and erases data to, from and in the optical record medium. More particularly, the invention relates to an optical data record/reproduction apparatus of which the optical head is capable of being moved accurately and at high speed.
An optical data record/reproduction apparatus as shown in FIG. 16, has been known in the art of record/reproduction apparatus. As shown, the optical data record/reproduction apparatus is provided with a light source "a", such as a semiconductor laser; a collimator "b" for converting diffusion laser light emitted from the light source "a" into parallel beams of laser light; a beam shaping prism "c" for shaping the spot shape of the laser beam from an elliptic shape to a substantially circular shape; a beam splitter "e" for splitting an incident laser beam to be incident on an optical record medium "d" and a reflected laser beam reflected by the optical record medium "d", one from the other; a 1/4.lambda. plate "f" for transforming the laser beam of linear polarization emanating from the beam splitter "e" into a laser beam of circular polarization; an objective lens "g", movably installed, for focusing the laser beams after passing through the 1/4.lambda. plate "f" at the focal plane on the optical record medium "d"; and a cylindrical lens "j" for directing the reflected laser beam split by the beam splitter "e" toward a quartered PIN photo diode "h" for producing a tracking error signal, a focusing error signal, and a reproduced RF signal.
In the optical data record/reproduction apparatus, data is recorded in the optical record medium "d" in a spiral fashion or a concentric circular fashion. To reproduce the stored data, an optical head incorporating an optical system thereinto, which includes the objective lens "g", for example, is moved in the radial direction of the optical record medium "d" (i.e., in the track direction). To cope with the problem of, for example, the plane inclination of the optical record medium "d", the optical head is moved in the direction orthogonal to the optical record medium "d" (i.e., in the focus direction). To realize this orthogonal movement, a drive system to be set forth below is used.
An example of the drive system will be described with reference to FIGS. 17 and 18. The drive system is provided with a movable table k1 shaped like an H in cross section; a linear bearing k3 and a carriage k2; paired bobbins k4 and k5; magnetic yokes k6 and k7; paired permanent magnets for track control m1, m2, and m3, m4, focus control permanent magnets m5 and m6; and magnetic holders k8. The movable table k1 is disposed near the optical record medium "d" and carries an optical head He thereon, which includes a focus control drive coil p1. The carriage k2, provided on the lower surface of the movable table k1, cooperates with the linear bearing k3 to movably support the movable table k1. The paired bobbins k4 and k5 are respectively provided on either side of the movable table k1 and have drive coils p2 for track control, which are respectively wound around the bobbins. The magnetic yokes k6 and k7 are respectively inserted into the tubular portions of the bobbins k4 and k5. For track control, paired permanent magnets m1, m2 and m3, m4 are respectively provided above and under the bobbins k4 and k5. The focus control permanent magnets m5 and m6 are disposed extending in the longitudinal direction of the permanent magnets m1 to m4. The magnetic holders k8 hold the permanent magnets m1 to m6. In the record/reproduction apparatus thus constructed, for the focus control, the optical head He is moved in the focus direction by an electromagnetic force developed when current is fed to the drive coil p1. For track control, the optical head He carried on the movable table k1 is moved in the direction of an arrow A by the electromagnetic force developed from each drive coil p2 when current is fed to a drive coils p2.
Another example of the conventional optical data record/reproduction apparatus is shown in FIG. 19. The record/reproduction apparatus is comprised of an optical head He, which is disposed near the optical record medium "d" and is configured to float by an air stream produced when the optical record medium "d" rotates. The record/reproduction apparatus of FIG. 19 includes a flat-spring like suspension n1 for supporting the optical head in a floating state, and a moving member n3 which supports the base end of the suspension n1 and is moved by a drive unit n2. In the apparatus, for track control, the optical head He is moved in the track direction by the moving member n3. For focus control, the floating action of the optical head He is used.
The optical data record/reproduction apparatus of FIGS. 17 and 18, formerly described, is constructed so as to perform the focus control by utilizing the focus control drive coil pl. Accordingly, the control system is complicated. Also in the apparatus, as shown in FIG. 18, the optical head He is disposed at a location apart from the drive source "k", which is made up of the movable table k1, carriage k2, bobbins k4 and k5, magnetic yokes k6 and k7, and the like. Accordingly, in operation, a moment tends to act on the optical head He. This makes the track control instable.
The optical data record/reproduction apparatus of FIG. 19 utilizes the floating action of the optical head He for the focus control. Accordingly, the control system is simplified in construction. However, also in the apparatus, the optical head He is disposed at a location apart from the drive source "n", which is made up of the drive unit n2, the moving member n3, and the like, in a manner that it is suspended from the drive source by means of the suspension n1. Accordingly, in operation, a moment also tends to act on the optical head He of FIG. 19. Hence, the apparatus of FIG. 19 also suffers from instability in track control.
To solve those problems, an optical data record/reproduction apparatus, as will be given below, has been proposed.
A proposed record/reproduction apparatus, as shown in FIGS. 20 through 22, is provided with a carriage q3 and a linear bearing q4, a pair of magnetic yokes q5 and q6, a drive unit "q" with permanent magnets q7 and q8, and an optical head He.
The carriage q3 and a linear bearing q4 are disposed under first and second movable members r1 and r2 located near the optical record medium. Each of the members is shaped like a tube with an elliptic cross section and consists of a drive coil q1 for track control and a bobbin q2 with a coil q1 wound therearound. The magnetic yokes q5 and q6 are respectively inserted through the tubes of the first and second movable members r1 and r2 and extended in the radial direction of the optical record medium. The drive unit "q" includes permanent magnets q7 and q8 which are disposed in the vicinity of the magnetic yokes q5 and q6 and extended in the longitudinal direction of the yokes. The optical head He is supported by resilient support member "s" extended between the first and second movable members r1 and r2. The head is caused to float by an air stream produced when the optical record medium rotates, and focuses converted light from a light source at the focal plane of the optical record medium. The optical head He is moved in the track direction when the first and second movable members r1 and r2 are moved by an electromagnetic force developed from the drive coil q1 when it is fed with current.
In the optical data record/reproduction apparatus, the floating action of the optical head He is utilized for focus control. This feature simplifies the control system. In the construction of the apparatus, the optical head He is disposed between the first and second movable members r1 and r2. This feature allows the optical head He to be disposed near the drive center. A moment acting on the optical head He is reduced, thereby stabling the track control.
The record/reproduction apparatuses as described above have the following problems, however. In the case of the apparatus shown in FIG. 20, to move the optical head He in the track direction of the optical record medium "d", a linear motor is driven, which, is made up of the drive coil q1 for track control, permanent magnets q7 and q8, and the like. At this time, current is fed to the drive coil q1, so that heat is generated in the coil. The generated heat is transferred through the resilient support member "s" to the optical head He and through the movable members r1 and r2 to the carriage q3. Accordingly, the head movable portion connected to the coil q1 tends to displace. Accordingly, the frequency characteristic when the optical head He is moved in the track direction of the optical record medium "d" deteriorates as shown in FIG. 23. This makes it difficult to control the optical head highly accurately. Accordingly, it is difficult to move the optical head He to a predetermined position quickly and accurately.
In the case of the record/reproduction apparatus shown in FIG. 19, the focus control is performed utilizing the air stream acting on the optical head He. This provides a simplified control system. The optical head He is mounted, by means of the flat-spring like suspension n1, at a location apart from the drive source including the drive unit n2, the moving member n3, and the like. With this construction, when the optical head He is moved, a moment acts on the optical head He, thereby hindering quick and accurate movement of the optical head to a desired position.
In the case of record/reproduction apparatus shown in FIGS. 20 and 21, the drive coil, the bearing, and the floating section are directly coupled with one another. Therefore, the heat generated in the drive coil owing to the current passage therethrough is transferred to the bearing and the floating section, possibly deteriorating the vibration characteristic of the optical head.